Steam dealkylation process

Abstract

Alkylaromatic hydrocarbons are dealkylated in a short cycle process characterized by a reaction period of 30-180 seconds followed by a regeneration period of 90-540 seconds--thus permitting attainment of improved conversion and yield of desired product.

We claim: 
     
       1. The method of steam dealkylating a charge alkylaromatic hydrocarbon which comprises passing a mixture consisting essentially of steam and charge alkylaromatic hydrocarbon into contact with a steam dealkylation catalyst at steam dealkylating reaction conditions for 30-180 seconds during which time the activity of the steam dealkylation catalyst, as measured by the mole percent conversion of charge alkylaromatic hydrocarbon to product dealkylated alkylaromatic hydrocarbon, decreases during the reaction period;   interrupting the flow of charge alkylaromatic hydrocarbon, thereby interrupting said reaction period, when the activity of said catalyst has decreased;   thereafter contacting said catalyst of decreased activity with steam during a regeneration period at regenerating conditions for 90-540 seconds, as the activity of said catalyst increases, thereby forming regenerated catalyst; and   recovering product dealkylated alkylaromatic hydrocarbon.   
     
     
       2. The method of steam dealkylating a charge alkylaromatic hydrocarbon as claimed in claim 1 wherein the ratio of regeneration time to reaction time is about 1-5:1. 
     
     
       3. The method of steam dealkylating a charge alkylaromatic hydrocarbon as claimed in claim 1 wherein the ratio of regeneration time to reaction time is about 3:1. 
     
     
       4. The method of steam dealkylating a charge alkylaromatic hydrocarbon as claimed in claim 1 wherein the regeneration time is about 180 seconds and the reaction time is about 60 seconds. 
     
     
       5. The method of steam dealkylating a charge alkylaromatic hydrocarbon as claimed in claim 1 wherein said charge alkylaromatic hydrocarbon contains toluene. 
     
     
       6. The method of steam dealkylating a charge alkylaromatic hydrocarbon as claimed in claim 1 wherein said charge alkylaromatic hydrocarbon contains a C 9  -C 11  hydrocarbon fraction. 
     
     
       7. The method of steam dealkylating a charge alkylaromatic hydrocarbon which comprises passing a mixture consisting essentially of steam and charge alkylaromatic hydrocarbon into contact with a steam dealkylation catalyst at steam dealkylating reaction conditions for 30-180 seconds during which time the activity of the steam dealkylation catalyst, as measured by the mole percent conversion of charge alkylaromatic hydrocarbon to product dealkylated alkylaromatic hydrocarbon, decreases to less than about 90% of the initial activity during a reaction period;   interrupting the flow of said charge alkylaromatic hydrocarbon, thereby interrupting said reaction period when the activity of said catalyst has decreased to less than about 90%;   thereafter contacting said catalyst of decreased activity with steam during a regeneration period at regenerating conditions for 90-540 seconds, as the activity of said catalyst increases to at least about 75% of the initial activity thereby forming regenerated catalyst; and   recovering product dealkylated alkylaromatic hydrocarbon.   
     
     
       8. The method of steam dealkylating a charge alkylaromatic hydrocarbon as claimed in claim 7 wherein the reaction period is interrupted when the activity of the catalyst is decreased to about 20%-90% of its initial activity. 
     
     
       9. The method of steam dealkylating a charge alkylaromatic hydrocarbon as claimed in claim 7 wherein the reaction period is interrupted when the activity of the catalyst has decreased to about 60%-85% of its initial activity. 
     
     
       10. The method of steam dealkylating a charge alkylaromatic hydrocarbon as claimed in claim 7 wherein the catalyst is regenerated during the regeneration period to an activity of 75%-100% of the initial activity. 
     
     
       11. The method of steam dealkylating a charge alkylaromatic hydrocarbon as claimed in claim 7 wherein said steam dealkylating reaction conditions and said regenerating conditions include temperature of 600° F.-950° F. and pressure of 0-400 psig. 
     
     
       12. The method of steam dealkylating a charge alkylaromatic hydrocarbon as claimed in claim 7 wherein the temperature and pressure are substantially the same during said reaction and said regeneration. 
     
     
       13. The method of steam dealkylating a charge alkylaromatic hydrocarbon as claimed in claim 7 wherein the flow of alkylaromatic hydrocarbon during said regeneration period is substantially interrupted during said regeneration period. 
     
     
       14. The method of steam dealkylating a charge alkylaromatic hydrocarbon as claimed in claim 7 wherein the flow of alkylaromatic hydrocarbon during said regeneration period is 0%-50% of the flow of said hydrocarbon during said reaction period. 
     
     
       15. The method of steam demethylating charge toluene which comprises passing a mixture consisting essentially of steam and toluene into contact with a steam demethylating catalyst at steam demethylating conditions including temperature of 600° F.-950° F. for 30-180 seconds during which time the activity of the steam demethylation catalyst, as measured by the mole percent conversion of charge toluene to product benzene, decreases during a reaction period;   interrupting the flow of toluene, thereby interrupting said reaction period when the activity of said catalyst has decreased;   thereafter contacting said catalyst of decreased activity with steam during a regeneration period at regenerating conditions including temperature of 600° F.-950° F., as the activity of said catalyst increases thereby forming regenerated catalyst; and   recovering product benzene.   
     
     
       16. The method of steam demethylating charge toluene as claimed in claim 15 which comprises passing a mixture consisting essentially of steam and toluene into contact with a steam demethylation catalyst at steam demethylating conditions including temperature of 600° F.-950° F. for 30-180 seconds during which time the activity of the steam demethylation catalyst, as measured by the mole percent conversion of charge toluene to product benzene has decreased to less than about 90% of the initial activity during a reaction period;   interrupting the flow of toluene, thereby interrupting said reaction period when the activity of said catalyst has decreased to less than about 90%;   thereafter contacting said catalyst of decreased activity with steam during a regeneration period at regenerating conditions including temperature of 600° F.-900° F., as the activity of said catalyst increased to at least about 75% of its initial activity thereby forming regenerated catalyst; and   recovering product benzene.   
     
     
       17. The method of steam demethylating charge toluene which comprises passing a mixture consisting essentially of steam and toluene into contact with a steam demethylation catalyst at steam demethylating conditions including temperatures of 650° F.-900° F., pressure of 0-200 psig, and steam to hydrocarbon mole ratio of 2-25:1 for 30-180 seconds during which time the activity of the steam demethylating catalyst, as measured by the mole percent conversion of charge toluene to product benzene decreases to 50-90% of its initial activity during a reaction period;   interrupting the flow of toluene, thereby interrupting said reaction period when the activity of said catalyst has decreased to a point at which the activity is less than 90% of the initial activity;   decreasing the flow of toluene to 0%-50% of that of the reaction period during a regenerating period;   therewith contacting said catalyst of decreased activity with steam at regenerating conditions including temperature of 650° F.-900° F., pressure of 0-400 psig, and a weight hourly space velocity WHSV of 0.1-10 for 90-540 seconds as the activity of said catalyst increases to 80%-100% of its initial activity thereby forming regenerated catalyst; and   recovering product benzene.   
     
     
       18. The method of steam dealkylating charge alkylaromatic hydrocarbon containing C 9  -C 11  hydrocarbon components which comprises passing a mixture consisting essentially of steam and charge into contact with a steam dealkylation catalyst at steam dealkylating conditions including temperature of 600° F.-950° F. for 30-180 seconds during which time the activity of the steam dealkylation catalyst, as measured by the mole percent conversion of charge alkylaromatic to product dealkylate decreases to less than about 90% of the initial activity during a reaction period;   interrupting the flow of charge alkylaromatic hydrocarbon thereby interrupting said reaction period when the activity of said catalyst has decreased to less than about 90%;   thereafter contacting said catalyst of decreased activity with steam during a regeneration period at regenerating conditions including temperature of 600° F.-900° F., as the activity of said catalyst increases to at least about 75% of its initial activity thereby forming regenerated catalyst; and   recovering product dealkylate.   
     
     
       19. The method of activating an unactivated steam dealkylation catalyst   a(VIII)2/n0:b(VI)2/m0:c(I).sub.2 0:d(Supp)     wherein a is 0.002-0.75; VIII represents a metal, having valence n of Group VIII of the Periodic Table; b is 0-0.78; c is 0.00003-0.17; VI represents a metal having valence m, of Group VIB of the Periodic Table; I represents a metal of Group I of the Periodic Table; d is 0.15-0.95; and Supp represents the catalyst support which comprises   (a) maintaining the unactivated catalyst in a hydrogen atmosphere at 950° F.-1400° F. for 2-10 hours thereby forming a hydrogen-treated catalyst;   (b) maintaining the hydrogen-treated catalyst in a steam-hydrogen atmosphere at 950° F.-1400° F. for 2-10 hours thereby forming a steamed hydrogen-treated catalyst;   (c) preferably cooling the steamed hydrogen-treated catalyst to 650° F.-900° F. in a steam or steam-hydrogen atmosphere thereby forming an activated catalyst; and   (d) recovering said activated catalyst.